The invention concerns a compound for the treatment of water containing metal ions and possibly other organic and/or inorganic pollutants, as well as a procedure for its production and its application in the separation of heavy and nonferrous heavy metals and dissolved, suspended or emulsified organic and/or inorganic components from aqueous systems.
Heavy and nonferrous heavy metals are widely used as components of alloys in steels and refined or corrosion resistant coatings in connection with synthetic or natural materials in all industrial countries. The technologies of modern industrial production produce, with the use of metals from the selection of the supplemental group of elements and some heavy metals of the third to fifth main group of the periodic system, apart from useful application, by their nature also a waste problem.
It is already known from R. Bauer, J. Wehling: "Thiocarbamide as precipitant for heavy metal sulfides" in Fresenius' Zeitschrift fur Analytische Chemie, 199th volume Springer-Verlag Berlin, 1964, pages 171 to 175, to treat metal ions with water, thiocarbamides and soda lye.
From DE-24 37 779-A1 a product and procedure for the removal of mercury and/or mercury salts from waste waters containing thiocarbamide and/or hydroxylamine salts, is also known.
In addition, a procedure for the processing of solutions containing copper and complexing agents, in which thiocarbamide is also used, is known from DE-26 08 153-A1.
Also known, from DE-22 42 473-A1, is a treatment procedure for a spent, currentless processing or stripping solution, in which sodiumhyposulfite is added.
Also known, from DE-21 22 415-A1, is a process for the detoxification, clarification and recovery of metal salts from waste waters and residual concentrates by reduction of the metals by means of hydrosulfite concentrate (sodiumhyposulfite) or hydrazine with the simultaneous application of an inoculating material [detoxifier] and sedimentation accelerator [enhancer] for the shortening of the precipitation time and reduction of the sludge volume, in which sodiumhyposulfite is used.
Also known, from DE-38 22 922-A1, is a procedure for the separation of heavy metals from waste waters, as well as preciptators for the execution of this procedure and procedures for the production of the precipitator, in which thiosulfates are used.
Also known, from Chemical Abstracts, Vol. 93, 1980, page 306, nr 93: 119741c is already the precipitation of ferrous cyanite from waste water, in which sodiumthiosulfates and sodiumhyposulfite are used among others.
From Pol. PL 125 519 in Chemical Abstracts, Vol. 101, 1984, page 276, nr 101: 59686k a procedure is already known for the detoxification of industrial waste waters, in which Na.sub.2 S.sub.2 O.sub.4 is used.
From JP 60-106585 (A) in Patents Abstracts of Japan, Seht G, 1985, Vol 9, nr 254 [C-308] a procedure is already known for the removal of heavy metals in which dithiocarbaminic acid is used among others.
From JP 75-72 451 in Chemical Abstracts, Vol. 83, 1975, page 279, nr 83: 197 620 v, a treatment of waste waters is already known which contains, among other things, citric acid.
From JP 75-72 867 in Chemical Abstracts, Vol. 84, 1976, page 281, nr 84: 35 077 s, a treatment of waste waters, containing, among other things, thiocarbamide is already known.
Also known, from DE-23 06 249-A1 is a procedure for the separation of toxic metal ions from waste water, in which a xanthate is used.
In addition, a procedure is known from DE-22 55 175-A1 for the reduction of dithiocarbamate content in waste waters.
Also known, from DE-23 12 233-B2, is a procedure for the removal of heavy metals from solutions, in which a polymer is used.
From DE-23 32 705-A1 a heavy metal binding agent, a procedure for its production and its application is known, whereby it contains a certain resin.
Finally, from U.S. Pat. No. 4,354,942, a procedure is known for the stabilization of mercury in mercury containing materials, which uses an inorganic sulfur compound of a certain kind.
After a careful estimate, some 5% of the produced or used metallic elements in production or processing procedures remain as remainders [residuals] or waste materials in pure form or in compounds, which, with the currently known methods, can in part not be recycled economically. Apart from economic aspects, which would make a low-cost technical recovery and thus reduction of the cost and currency needs for the acquisition of raw materials, as well as a stretching of the raw material resources desirable, the ecological aspects of volume reduction of special refuse, particularly the heavy and non-ferrous heavy metals that have toxic effects on almost all biological species, are important.
The removal of toxic heavy and non-ferrous heavy metal from the waste water of the metal processing industry is still done to a large extent by the classical method of hydroxide precipitation with soda lye, milk of lime or, in special cases, with sodium carbonate. Based on the wide pH-range into which the hydroxides and oxyhydrates fall, and based on mixed reactions, e.g. of various bivalent metals with similar ion radii, it is necessary, however, to determine for each metal ion mixture the optimal "compromise" pH-value empirically by advanced testing, as a great number of factors influence and overshadow the process of precipitation. The hydroxide precipitation of heavy and non-ferrous heavy metals has, in principle, four other substantial disadvantages:
1. The solubility products of the metal hydroxides are by at least 7 to 10 powers of ten greater than those of the corresponding sulfides. The solubility of the metal hydroxides also is an estimate, depending on the matrix proportion of the solutions, up to the value of ten million times higher than that of the corresponding sulfides.
2. The neutral salt influence in the precipitation medium, which leads to the increase of the solubility, has a considerably stronger effect with hydroxide precipitation than with sulfide precipitation. In addition, a negative influence on the sedimentation behavior and filterability of the precipitate can often be observed.
3. Hydroxide precipitation of some heavy and non-ferrous heavy metals in the presence of complexing agents is not at all possible or only to an unsatisfactory extent.
4. The metal hydroxides precipitated according to this classical method can only be recycled by using difficult and costly methods. For this reason, hydroxide sludges from the metal processing industry are up to now usually disposed of as special [i.e., hazardous] waste at high costs.
Contrary to this, the solubility products of most metal sulfides are so low that the quantitative precipitation of the metal ions themselves occurs from solutions that are strongly complexing agent containing. In spite of this, sulfide precipitation is rarely performed in the area of waste water. On the one hand, the use of the unpleasantly smelling, toxic and flammable hydrogen sulfide is not without its problems and, on the other hand, most of the metal sulfides have an unsatisfactory precipitation from the aqueous phase.
In the practice of waste water purification, various organic sulfides have been introduced for special applications within recent years. The organic sulfides work according to the same principle as the sulfides and precipitate, among others, copper, cadmium, mercury, lead, nickel, tin and zinc as sulfides. However, their disadvantage is due to the fact that the admissible pH-value is limited to values of above 7 as in the acid range the ineffective precipitation of free acid takes place.
However, the stability constants of many heavy metal complexes, particularly from the type of the often used polyamine carbonic acids, are especially dependent on pH-values to the extent that with higher pH-values a greater stability occurs than in the acidic range. The precipitation of complexed metals is then only possible with a complicated procedure by means of decomplexing with iron-III ions.
However, in the complete absence of complexing agents and with strict enforcement of the optimal operating conditions, it is possible to just remain below the new limit values of the 40th General Administrative Regulation on Minimum Requirements for Running Waste Water into Bodies of Water [receiving water] according to .sctn.7a of the Water Management Law (WHG=Wasserhaushaltsgesetz), using hydroxide precipitation if an additional filtration of the treated waste waters is also done. Such an operation is, however, very costly and provides no guarantee for a constant following of legal regulations as the security range between the attainable values and the limit values is too narrow with a factor of about 1.5 to 2. Even the smallest malfunctions lead in these cases to an exceeding of the admissible values.
In the precipitation of heavy and non-ferrous heavy metals with polysulfides, the toxic hydrogen sulfides are replaced by alkaline or alkaline earth polysulfides. However, the disadvantage of the polysulfide precipitation agents known to-date is that they have a poor solubility in water and thus require an increase in material with the according cost increase.
In addition, the customary precipitation means have the disadvantage that they are mainly confined to the acid pH-range. A precipitation of heavy metal ions from very acid media and from strongly alkali media with the same precipitation agent has so far not been successful.